1.It is due to condensation.
2.Condensation is the phase change from gas to liquid.
3.When a cold soft drink bottle is kept in open air,the water vapour present in the surrounding air condenses on the bottle.
4.The water molecules are slowed down and stick to the surface of the bottle as its surface is cold.
5.These water droplets are seen as dew on the surface of the bottle.
We get dew on the surface of a cold soft drink bottle kept in open air because the vapours present in the air, when come in contact with the cold surface, get condensed (cooled) to form water droplets which appear as dew.